Method for producing a mating-type connecting part

ABSTRACT

A copper sheet is adjusted to have arithmetic mean roughness Ra of from 0.5 μm to 4.0 μm in a direction parallel to a sliding direction upon connection, mean projection-depression interval of from 0.01 mm to 0.3 mm in the direction, skewness of less than 0, and protrusion peak portion height of 1 μm or less. A Sn surface coating layer group X as a plurality of parallel lines is included, and a Cu—Sn alloy coating layer is adjacent to each side of each Sn coating layer. Maximum height roughness is 10 μm or less in a direction of part insertion. The sheet is surface-roughened by pressing when stamped, thereby forming depressions as a plurality of parallel lines in its surface. The sheet is then plated with Cu and Sn, followed by reflowing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrically conductive material forconnecting parts, such as a terminal for connectors or a bus bar usedmainly for electrical wiring in automobiles, household equipment, andthe like, and also to a mating-type connecting part and a method forproducing the same. The present invention particularly relates to anelectrically conductive material for connecting parts and a mating-typeconnecting part, which are expected to have both reduced friction orabrasion upon the insertion and extraction of male and female terminalsand electrical connection reliability in use, and a method for producingthe same.

2. Description of the Related Art

JP-B-3926355 describes an electrically conductive material forconnecting parts, which has high electrical reliability (low contactresistance) and a low friction coefficient and is suitable as a terminalfor a mating-type connector. According to the invention of JP-B-3926355,a copper-alloy plate strip having higher surface roughness than ordinarycopper-alloy plate strips is used as a base material, and, on thesurface of the base material, a Ni plating layer, a Cu plating layer,and a Sn plating layer are formed in this order, a Cu plating layer anda Sn plating layer are formed in this order, or only a Sn plating layeris formed. The Sn plating layer is reflowed so that a Cu—Sn alloy layeris formed from the Cu plating layer and the Sn plating layer or from thecopper alloy base material and the Sn plating layer. At the same time, aportion of the Cu—Sn alloy layer is allowed to expose on the surfacethrough the Sn plating layer smoothed by reflowing (a portion of theCu—Sn alloy layer is exposed in the area of projections of thedepressions and projections formed on the base material surface).

In JP-B-3926355, the electrically conductive material for connect partsformed after reflowing has, as a surface coating layer, a Cu—Sn alloylayer and a Sn layer, or alternatively a Ni layer, a Cu—Sn alloy layer,and a Sn layer, in this order. In some cases, a Cu layer remains betweenthe base material surface and the Cu—Sn alloy layer or between the Nilayer and the Cu—Sn alloy layer. According to JP-B-3926355, the Cu—Snalloy layer and the Sn layer are formed on the outermost surface (theCu—Sn alloy layer exposure area ratio on the surface is 3 to 75%), theaverage thickness of the Cu—Sn alloy layer is 0.1 to 3.0 μm, the Cucontent is 20 to 70 at %, and the Sn layer has an average thickness of0.2 to 5.0 μm. It is also mentioned that the arithmetic mean roughnessRa of the base material surface is 0.15 μm or more at least in onedirection, and is preferably 4.0 μm or less in every direction, and thatthe Cu—Sn alloy layer exposure interval on the surface is preferably0.01 to 0.5 mm at lease in one direction.

JP-B-4024244 describes an electrically conductive material forconnecting parts, which is the subordinate concept of JP-B-3926355, anda method for producing the same. The plating layer configuration and thecoating layer configuration after reflowing themselves are the same asin JP-B-3926355. According to JP-B-4024244, in the electricallyconductive material for connecting parts formed after reflowing, a Cu—Snalloy layer and a Sn layer are formed on the outermost surface (of thesurface coating layer, the Cu—Sn alloy layer exposure area ratio on thesurface is 3 to 75%), the Cu—Sn alloy layer has an average thickness of0.2 to 3.0 μm and a Cu content of 20 to 70 at %, the Sn layer has anaverage thickness of 0.2 to 5.0 μm, and the arithmetic mean roughness Raof the base material surface is 0.15 μm or more at least in onedirection and is 3.0 μm or less in every direction. It is also mentionedthat the arithmetic mean roughness Ra of the base material surface is0.3 μm or more at least in one direction, and is preferably 4.0 μm orless in every direction, and that the Cu—Sn alloy layer exposureinterval on the surface is preferably 0.01 to 0.5 mm at lease in onedirection.

JP-A-2007-258156 describes an electrically conductive material forconnecting parts, which basically inherits the technical concepts ofJP-B-3926355 and JP-B-4024244 and has improved solderability, and amethod for producing the same. In the invention, the plating layerconfiguration and the coating layer configuration after ref lowingthemselves are basically the same as in JP-B-3926355 and JP-B-4024244.However, unlike JP-B-3926355 and JP-B-4024244, the invention mayencompass the case where the Cu—Sn alloy layer is not exposed (only a Snlayer is present on the outermost surface). In this application, anelectrically conductive material for connecting parts formed after reflowing is specified as follows. Of the surface coating layer, the Nilayer has an average thickness of 3.0 μm or less, the Cu—Sn alloy layerhas an average thickness of 0.2 to 3.0 μm, the Sn layer has, in avertical cross-section of the material, a minimum inscribed circlediameter (D1) of 0.2 μm or less and a maximum inscribed circle diameter(D2) of 1.2 to 20 μm, and the altitude difference (Y) between theoutermost point of the material and the outermost point of the Cu—Snalloy layer is 0.2 μm or less. JP-A-2007-258156 further mentions that itis preferable that when (D1) is 0 μm (when a portion of the Cu—Sn alloylayer is exposed, and the outermost surface is formed of the Cu—Sn alloylayer and the Sn layer), the Cu—Sn alloy layer has a maximum inscribedcircle diameter (D3) of 150 μm or less on the material surface and/orthe Sn layer has a maximum inscribed circle diameter (D4) of 300 μm orless on the material surface.

Meanwhile, JP-A-2004-300524, JP-A-2005-105307 and JP-A-2005-183298 statethat a copper-alloy plate strip is stamped and then entirely plated withSn, i.e., post-plated, so that a Sn plating layer is formed also on thestamped end face, thereby improving the solderability of a terminal orthe like as compared with the case where a copper-alloy plate strip isplated with Sn prior to stamping (pre-plated).

Further, JP-A-2008-269999 and JP-A-2008-274364 mention that apost-plated terminal has improved electrical reliability (low contactresistance), a reduced friction coefficient at a mating portion, andalso improved solderability at a soldering portion.

According to the invention of JP-A-2008-269999, a terminal is formed insuch a manner that only a mating portion has increased surfaceroughness, and then a Ni plating layer, a Cu plating layer, and a Snplating layer are formed in this order, a Cu plating layer and a Snplating layer are formed in this order, or only a Sn plating layer isformed. The Sn plating layer is reflowed so that a Cu—Sn alloy layer isformed from the Cu plating layer and the Sn plating layer or from thecopper alloy base material and the Sn plating layer. At the same time, aportion of the Cu—Sn alloy layer is allowed to expose on the surfacethrough the Sn plating layer smoothed by ref lowing (a portion of theCu—Sn alloy layer is exposed in the area of projections of thedepressions and projections formed on the base material surface). Atthis time, the plating thickness is the same over the entire surface. Atthe mating portion, the Cu—Sn alloy layer and the Sn layer are formed onthe outermost surface (the Cu—Sn alloy layer is exposed on the surface),and, therefore, there is a problem in terms of solder wettability.However, at other portions than the mating portion, there are nodepressions or projections. Therefore, no Cu—Sn alloy layer is exposed(only a Sn layer is present on the outermost surface), and solderwettability is thus excellent.

According to the invention of JP-A-2008-274364, a copper alloy materialwith high surface roughness is stamped into a terminal piece, and then aNi plating layer, a Cu plating layer, and a Sn plating layer are formedin this order, a Cu plating layer and a Sn plating layer are formed inthis order, or only a Sn plating layer is formed. The Sn plating layeris reflowed so that a Cu—Sn alloy layer is formed from the Cu platinglayer and the Sn plating layer or from the copper alloy base materialand the Sn plating layer. At the same time, a portion of the Cu—Sn alloylayer is allowed to expose on the surface through the Sn plating layersmoothed by ref lowing (a portion of the Cu—Sn alloy layer is exposed inthe area of projections of the depressions and projections formed on thebase material surface). In this case, the Sn plating layer at thesoldering portion is formed thick. As a result, the Cu—Sn alloy layer isnot exposed on the surface at the soldering portion, leading toexcellent solder wettability.

SUMMARY OF THE INVENTION

The electrically conductive materials for connecting parts described inJP-B-3926355, JP-B-4024244, JP-A-2007-258156, JP-A-2008-269999 andJP-A-2008-274364 have high electrical reliability (low contactresistance) and a low friction coefficient, and thus are suitable asterminals for mating-type connectors. However, strict requirements areimposed on the reduction of terminal insertion force due to theminiaturization or multipolarization of terminals, and there is a demandfor provision of a material that can achieve a lower-insertion-forceterminal corresponding to the miniaturization of terminals and also forfurther improvement of electrical reliability.

An object of the present invention is, in order to meet such demands, tofurther improve the techniques of the patent documents mentioned above,and provide an electrically conductive material for connecting parts,which achieves lower insertion force in response to the miniaturizationof terminals and has improved electrical reliability.

Further, in the electrically conductive materials for connecting partsdescribed in JP-B-3926355, JP-B-4024244, JP-A-2007-258156,JP-A-2008-269999 and JP-A-2008-274364, a surface-roughened copper sheetis used as a base material, and a Ni plating layer, a Cu plating layer,and a Sn plating layer, for example, are formed in this order on thesurface thereof. Also, the Sn plating layer is reflowed to form a Cu—Snalloy coating layer from the Cu plating layer and the Sn plating layer,and, at the same time, a portion of the Cu—Sn alloy coating layer isexposed on the surface through the Sn coating layer smoothed by reflowing.

As exposure indices of a Sn coating layer and a Cu—Sn coating layer, theexposure area ratio and average exposure interval of a Cu—Sn alloycoating layer (JP-B-3926355 and JP-B-4024244) and the maximum inscribedcircle diameter and maximum circumscribed circle diameter of a Sncoating layer (JP-A-2007-258156) have been specified.

Meanwhile, no special attention has been paid to the shape of anindividual Sn coating layer or Cu—Sn alloy coating layer. However, inorder to deal with further miniaturization of terminals, in addition tothe above indices, which are rather abstract, an appropriate andcontrollable plan-view shape will be necessary for the specific shape ofan individual Sn coating layer or Cu—Sn alloy coating layer.

Accordingly, the present invention is aimed to provide a mating-typeconnecting part that includes a Sn coating layer or Cu—Sn alloy coatinglayer with an appropriate and controllable plan-view shape and iscapable of dealing with the miniaturization of terminals.

A copper sheet for connecting parts according to the present inventionhas a surface roughness defined by an arithmetic mean roughness Ra of0.5 μm or more 4.0 μm or less in a direction parallel to a slidingdirection upon connection, a mean projection-depression interval RSm of0.01 mm or more and 0.3 mm or less in said direction, a skewness Rsk ofless than 0, and a protrusion peak portion height Rpk of 1 μm or less.It is preferable that the copper sheet preferably has a protrusionvalley portion depth Rvk of 2 μm or more and 15 μm or less in thedirection parallel to the sliding direction. The copper sheet forconnecting parts has a Cu—Sn alloy coating layer and a Sn or Sn alloycoating layer formed on the outermost surface thereof, and therebyserves as an electrically conductive material for connecting parts. Thesurface comes in slidable contact with a mating material.

The copper sheet (base material) for connecting parts has a Cu—Sn alloycoating layer and a Sn or Sn alloy coating layer (the two arecollectively referred to as a Sn coating layer) formed on the outermostsurface thereof as a surface coating layer. The specific configurationof the surface coating layer is not limited, but is preferably suchthat, for example, as described in JP-B-3926355, JP-B-4024244 andJP-A-2007-258156, the Cu—Sn alloy coating layer and the Sn coating layerare formed in this order, and a portion of the Cu—Sn alloy coating layeris exposed on the outermost surface. It is preferable that the Sncoating layer is smoothed by ref lowing.

As a part of the surface coating layer of the copper sheet forconnecting parts, a Ni coating layer may be formed between the surfaceof the copper sheet for connecting parts and the Cu—Sn alloy coatinglayer, and a Cu coating layer may be further formed between the Nicoating layer and the Cu—Sn alloy coating layer. Further, a Cu coatinglayer may be formed between the surface of the copper sheet forconnecting parts and the Ni coating layer.

In the present invention, the copper sheet for connecting parts includesa copper or copper-alloy plate strip (plate and strip). The Sn coatinglayer, the Cu coating layer, and the Ni coating layer contain a Snalloy, a Cu alloy, and a Ni alloy, respectively, in addition to the Sn,Cu, and Ni metals.

As described in JP-B-3926355, JP-B-4024244 and JP-A-2007-258156, theelectrically conductive material for connecting parts can be produced byforming, on the surface of the base material formed of a copper sheet(having the above surface roughness), a Cu plating layer and a Sn or Snalloy plating layer (the two are hereinafter collectively referred to asa Sn plating layer) in this order, followed by ref lowing to form aCu—Sn alloy coating layer and a Sn coating layer in this order.

The Cu—Sn alloy coating layer is formed by the interdiffusion of Cu andSn of the Cu plating layer and the Sn plating layer caused by reflowing. At that time, the Cu plating layer may entirely disappear orpartially remain. When the Cu plating layer partially remains, a Cucoating layer is formed between the surface of the copper sheet and theCu—Sn alloy coating layer. Depending on the thickness of the Cu platinglayer, Cu may also be supplied from the copper sheet (base material).

It is preferable that the Cu plating layer formed on the surface of thecopper sheet (base material) has an average thickness of 1.5 μm or less,and the Sn plating layer has an average thickness within a range of 0.3to 8.0 μm. The average thickness of the Cu plating layer is preferably0.1 μm or more.

In the production method mentioned above, no Cu plating layer may beformed. In such a case, Cu for the Cu—Sn alloy coating layer is suppliedfrom the copper sheet (base material).

In the production method mentioned above, a Ni plating layer may beformed between the surface of the copper sheet (base material) and theCu plating layer. In such a case, it is preferable that the Ni platinglayer has an average thickness of 3 μm or less, and the Cu plating layerhas an average thickness of 0.1 to 1.5 μm. A further Cu plating layermay also be formed between the surface of the copper sheet (basematerial) and the Ni plating layer.

In the copper sheet (base material), the region to have the abovesurface roughness and form the surface coating layer may entirely coverone or both surfaces of the base material or may occupy only a portionof one or both surfaces.

In the present invention, the Cu plating layer, the Sn plating layer,and the Ni plating layer contain a Cu alloy, a Sn alloy, and a Ni alloy,respectively, in addition to the Cu, Sn, and Ni metals.

As used herein, a “coating layer” refers to each of the layersconstituting a surface plating layer after reflowing, while a “platinglayer” refers to each of the layers constituting a surface plating layerbefore ref lowing.

A mating-type connecting part according to the present invention isobtained by post-plating and ref lowing a copper sheet stamped into apredetermined shape, and includes a mixture of a Cu—Sn alloy coatinglayer and a Sn coating layer on an outermost surface thereof on the sidethat is in contact with a mating part. The Sn coating layer is smoothedby reflowing. The mating-type connecting part has the followingcharacteristics:

(1) the Sn coating layer includes a Sn coating layer group observed as aplurality of parallel lines, the Cu—Sn alloy coating layer is presentadjacent to each side of each of Sn coating layers constituting the Sncoating layer group, and the maximum height roughness Rz of the surfaceis 10 μm or less in the direction of part insertion; or

(2) the Sn coating layer includes a Sn coating layer group observed as aplurality of parallel lines and one or more additional Sn coating layergroups each observed as a plurality of parallel lines, the Sn coatinglayer groups cross each other in a grid pattern, the Cu—Sn alloy coatinglayer is present adjacent to each side of each of Sn coating layersconstituting each Sn coating layer group, and the maximum heightroughness Rz of the surface is 10 μm or less in the direction ofterminal insertion.

In the mating-type connecting part, it is preferable that the Sn coatinglayers of each Sn coating layer group have a width of 1 to 500 μm, and,of the Sn coating layers of each Sn coating layer group, the intervalbetween adjacent Sn coating layers is 1 to 2000 μm.

As mentioned above, the Sn coating layers of each Sn coating layer groupare individually observed as a plurality of parallel lines on theoutermost surface on the side that is contact with a mating part(sliding side). However, such Sn coating layers do not necessarily haveto be in the form of mathematically parallel lines. Even when the Sncoating layers of each Sn coating layer group are individually curvy,wavy, or winding in practically the same form, such a case is alsoencompassed by the present invention.

The mating-type connecting part has a Cu—Sn alloy coating layer and a Sncoating layer formed on the outermost surface thereof as a surfacecoating layer of the copper sheet (base material). The specificconfiguration of the surface coating layer formed of the Cu—Sn alloycoating layer and the Sn coating layer may be such that, for example, asdescribed in JP-B-3926355, JP-B-4024244 and JP-A-2007-258156, the Cu—Snalloy coating layer and the Sn coating layer are formed in this order,and a portion of the Cu—Sn alloy coating layer is exposed on theoutermost surface through the Sn coating layer smoothed by ref lowing.In this case, the Cu—Sn alloy coating layer exposed on the outermostsurface is measured as a peak of a roughness curve, and such a peak isreflected by the magnitude of maximum height roughness Rz.

When the Cu—Sn alloy coating layer and the Sn coating layer are formedin this order, it is preferable that the Cu—Sn alloy coating layer hasan average thickness of 0.1 to 3 μm, and the Sn coating layer has anaverage thickness of 0.2 to 5.0 μm. Such average thicknesses of coatinglayers are on the same level as those of related art (JP-B-3926355,JP-B-4024244 and JP-A-2007-258156).

As a part of the surface coating layer of the mating-type connectingpart, a Ni coating layer may be formed between the surface of the coppersheet (base material) and the Cu—Sn alloy coating layer, and a Cucoating layer may be further formed between the Ni coating layer and theCu—Sn alloy coating layer. A Cu coating layer may further be formedbetween the surface of the copper sheet for connecting parts and the Nicoating layer.

The present invention provides an electrically conductive material forconnecting parts, which achieves low insertion force in response to theminiaturization of terminals and has excellent electrical reliability.

The present invention also provides a mating-type connecting part thatachieves low insertion force and has excellent electrical reliability.

The plan-view shapes of the Sn coating layer and the Cu—Sn alloy coatinglayer specified by the present invention are compatible with theminiaturization of terminals. Further, the plan-view shapes can beeasily controlled by suitably roughening the surface of the coppersheet.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a roughness curve (JIS B0601) of No. 1 in Examples;

FIG. 2 is an amplitude curve calculated from the roughness curve of FIG.1;

FIG. 3 is a load curve calculated from the roughness curve (JIS B0671-1)of FIG. 1;

FIG. 4 is a schematic diagram showing an example of a surface-rougheningmethod for obtaining the surface roughness specified by the presentinvention;

FIG. 5 is a plan view of a copper sheet after surface roughening in theExamples;

FIG. 6 is a surface SEM (composition image) of a specimen No. 1 in theExamples;

FIG. 7 is a schematic diagram of a jig for use in a friction coefficientevaluation test in the Examples;

FIG. 8A is a schematic plan view illustrating the configuration of thesurface coating layer of a mating-type connecting part according to thepresent invention;

FIG. 8B is a schematic plan view illustrating the configuration of thesurface coating layer of a mating-type connecting part according to thepresent invention;

FIG. 9A is another schematic plan view illustrating the configuration ofthe surface coating layer of a mating-type connecting part according tothe present invention;

FIG. 9B is another schematic plan view illustrating the configuration ofthe surface coating layer of a mating-type connecting part according tothe present invention;

FIG. 10A is a schematic cross-sectional view illustrating theconfiguration of the surface coating layer of a mating-type connectingpart according to the present invention;

FIG. 10B is a schematic cross-sectional view illustrating theconfiguration of the surface coating layer of a mating-type connectingpart according to the present invention;

FIG. 11A is a schematic cross-sectional view illustrating the surfaceroughening of a copper sheet in use for a mating-type connecting partaccording to the present invention;

FIG. 11B is a schematic cross-sectional view illustrating the surfaceroughening of a copper sheet in use for a mating-type connecting partaccording to the present invention;

FIG. 12 is a plan view of a copper sheet after surface roughening in theExamples;

FIG. 13A is a roughness curve of a specimen No. 101 in the Examples;

FIG. 13B is a surface SEM (composition image) of a specimen No. 101 inthe Examples; and

FIG. 14 is a schematic diagram of a jig for use in a frictioncoefficient evaluation test in the Examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an electrically conductive material for connecting partsaccording to the present invention will be described in detail.

Generally, in consideration of electrical reliability, corrosionresistance, etc., an electrically conductive material for connectingparts is plated with Sn or a Sn alloy. A conventionally used Sn platinglayer applied to an electrically conductive material for connectingparts has an average thickness of about 1 μm. In the case of Sn platingon a copper base material, a Cu—Sn alloy coating layer is formed at theinterface between the Sn plating and the copper of the base material,and, therefore, the remaining Sn plating layer (Sn coating layer) has athickness of about 0.4 μm. When the Sn coating layer has a thickness ofless than 0.4 μm, this leads to a decrease in heat-resistancereliability (electrical characteristics) and corrosion resistance.Meanwhile, when the Sn coating layer has a larger thickness, this leadsto an increase in insertion force upon terminal connection, decreasingworkability.

For the purpose of reducing such terminal insertion force, theelectrically conductive material for connecting parts according to thepresent invention has a hard Cu—Sn alloy coating layer exposed on theoutermost surface thereof. That is, a Cu—Sn alloy coating layer and a Sncoating layer are present on the outermost surface.

The copper sheet material, which is a plating base material for theelectrically conductive material for connecting parts, has the specificsurface roughness mentioned above. Unless otherwise noted, the surfaceroughness is a parameter defined by JIS B0601 or JIS B0671.

The following describes the reason why the arithmetic mean roughness Rashould be 0.5 μm or more and 4.0 μm or less in the direction parallel tothe sliding direction upon connection. The arithmetic mean roughness Rais a value obtained by sampling a reference length L from a roughnesscurve in the direction of its mean line, summing the absolute values ofdeviations of the sampled portion from the mean line to the measuredcurve, and averaging the sum and is less likely to be affected bypeculiar parts such as cracks and foreign matters, and thus the obtainednumerical value is stable. Generally, the magnitude of surface roughnessis represented by the magnitude of the value of arithmetic meanroughness Ra. JP-B-3926355 and JP-B-4024244 also use arithmetic meanroughness Ra to specify surface roughness. The direction parallel to thesliding direction upon connection refers to, in the case of amating-type terminal, the direction in which a terminal is inserted.FIG. 1 shows one of roughness curves obtained in Examples (according toJIS B0601).

When the arithmetic mean roughness Ra is less than 0.5 μm in thedirection parallel to the sliding direction upon connection, the surfaceof the base material has small projections and depressions. Accordingly,in the case where the Sn coating layer has a thickness of more than 0.4μm, when the skewness Rsk is less than 0 in the above direction, theCu—Sn alloy coating layer is not exposed on the outermost surface, andthis results in a friction coefficient of more than 0.4 as measured bythe measurement method mentioned below. In the case where the arithmeticmean roughness Ra is 0.5 μm or more in the above direction, even whenthe Sn coating layer has a thickness of more than 0.4 μm and is as thickas 0.7 μm, a friction coefficient of 0.4 or less can be ensured.Meanwhile, when the arithmetic mean roughness Ra is more than 4.0 μm,this makes it difficult to smooth the material surface by the flowingaction of the molten Sn or Sn alloy plating during reflowing. Therefore,the arithmetic mean roughness Ra should be 0.5 μm or more and 4.0 μm orless in the above direction. It is preferable that the arithmetic meanroughness Ra is 4.0 μm or less in every direction.

The following describes the reason why the mean projection-depressioninterval RSm in the direction parallel to the sliding direction uponconnection should be 0.01 to 0.3 mm. Mean projection-depression intervalRSm is a value obtained by sampling a reference length L from aroughness curve in the direction of its mean line, calculating the totallength of the mean lines each corresponding to one peak and one valleyadjoining thereto, and expressing the average thereof in millimeters.The value of mean projection-depression interval RSm can be calculatedfrom the roughness curve from which the arithmetic mean roughness Ra iscalculated. The mean projection-depression interval RSm of the surfaceof the copper sheet is a value that directly reflects the exposureintervals of the Cu—Sn alloy coating layer. When RSm is less than 0.01mm, the exposure intervals of the Cu—Sn alloy coating layer are narrow.As a result, the oxidation of Cu is promoted in high-temperatureenvironments, causing an increase in contact resistance. When the meanprojection-depression interval RSm is more than 0.3 mm, the exposureintervals of the Cu—Sn alloy coating layer are wide, causing anincreased friction coefficient in a small-sized terminal with a smallelectrical contact portion. In the case where a terminal is small-sized,the contact portion accordingly has a small contact area. When theexposure intervals of the Cu—Sn alloy coating layer are wide, contactoccurs at the Sn coating layer zones therebetween. Therefore, the zoneof contact undergoes sliding between Sn and Sn to cause adhesion,increasing the friction coefficient. Therefore, the meanprojection-depression interval RSm should be 0.01 or more and 0.3 mm orless.

The following describes the reason why the skewness Rsk should be lessthan 0 in the above direction. Skewness Rsk is a value that representsthe relativity of an amplitude curve calculated from a roughness curveto its mean line. The value of skewness Rsk can be calculated from theroughness curve from which the arithmetic mean roughness Ra iscalculated. An amplitude curve shows, on a graph, all cut levels in aroughness curve together with the probability that the roughness curveequals the cut levels. Rsk<0 when the probability is biased above themean line, Rsk>0 when it is biased below the mean line, and Rsk=0 whenit matches the mean line. In the case where the arithmetic meanroughness Ra and the mean projection-depression interval RSm are withinthe ranges specified above, when Rsk is not less than 0 (Rsk≧0), thezone of depressions increase, leading to an increase in the area of theSn coating layer. That is, the zone of contact undergoes sliding betweenSn and Sn, increasing the friction coefficient. Therefore, the skewnessRsk should be less than 0 (Rsk<0). A range where Rsk≧−3.00 can be easilyachieved by the surface-roughening method mentioned below. FIG. 2 showsan amplitude curve calculated from the roughness curve of FIG. 1. Inthis example, the probability is higher above the mean line (in aposition at a cut level of 50%).

The following describes the reason why the protrusion peak portionheight Rpk should be 1 μm or less in the above direction. Protrusionpeak portion height Rpk is specified by JIS B0671-2. This is a valuethat represents the mean height of protrusion peak portions located onthe core sections in a roughness curve, and is determined from a loadcurve calculated from the roughness curve specified by JIS B0671-1. Rpkcan be determined from a load curve calculated from the roughness curvefrom which the arithmetic mean roughness Ra is determined (however, theprocessing should follow JIS B0671-1). Such a protrusion peak portion isa peak portion that further protrudes from a peak for defining RSm. Withreference to FIG. 1, protrusion peak portions are finely formed on theroughness curve peaks themselves, so the intervals between theprotrusion peak portions are smaller than RSm, the mean interval ofpeaks (valleys). After Sn plating by reflowing process, a Cu—Sn alloycoating layer is formed in such an area, resulting in a reduced frictioncoefficient. However, when the protrusion peak portion height Rpk ismore than 1 μm, the height of the Cu—Sn alloy coating layer protrudingfrom the material surface is increased. Such a protruding Cu—Sn alloycoating layer shaves the Sn coating layer on the embossed surface, andthis leads to an increase in insertion force. Therefore, the protrusionpeak portion height Rpk should be 1 μm or less. Rpk is preferably 0.3 μmor more and 1 μm or less; in such a case, even when the female terminalhas an emboss diameter as small as 1.0 mm and the Sn coating layer has athickness as large as 0.7 μm, a friction coefficient of 0.4 or less asmeasured by the measurement method mentioned below can be achieved. FIG.3 shows a load curve calculated from the roughness curve shown in FIG.1.

The following describes the reason why the protrusion valley portiondepth Rvk should be 2 to 15 μm in the above direction. Protrusion valleyportion depth Rvk is specified by JIS B0671-2. This is a value thatrepresents the mean depth of protrusion valley portions located underthe core sections in a roughness curve, and is determined from a loadcurve calculated from the roughness curve. Rvk can be determined fromthe load curve from which the protrusion peak portion height Rpk isdetermined. When the mean depth of protrusion valley portions is large,molten Sn flows thereinto during ref lowing. Accordingly, with the Cu—Snalloy layer being exposed on the surface, the average thickness of theSn coating layer can be increased. That is, in the case where thearithmetic mean roughness Ra, mean projection-depression interval RSm,skewness Rsk, and protrusion peak portion height Rpk are within theranges specified above, and the protrusion valley portion depth Rvk is 2or more, even when the Sn coating layer is as thick as 1.0 μm, afriction coefficient of 0.4 or less can be achieved. Meanwhile, when theprotrusion valley portion depth Rvk is set at more than 15 μm by thesurface-roughening method mentioned below, this is likely to causebending or deformation of the copper sheet. Therefore, the protrusionvalley portion depth Rvk should be 2 to 15 μm.

For the measurement of the surface roughness of the copper sheet, theparameters may be determined as follows. On the surface of the coppersheet, a region with a width corresponding to a terminal is suitablyselected, and, within such a region, measurements are made at severalpoints along the direction parallel to the sliding direction uponconnection. Based on the roughness curve that provides the maximumarithmetic mean roughness Ra, each surface roughness parameter may bedetermined.

As a surface film layer formed on the material surface, the surface filmlayer structure described in JP-B-3926355 and JP-B-4024244 may beapplied. That is, a Cu—Sn alloy coating layer with a Cu content of 20 to70 at % and an average thickness of 0.2 to 3.0 μm and a Sn coating layerwith an average thickness of 0.2 to 5.0 μm are formed in this order, anda portion of the Cu—Sn alloy coating layer is exposed on the surface ofthe Sn coating layer, with the exposure ratio on the material surfacebeing 3 to 75%. Further, a Ni coating layer and a Cu layer may be formedbetween the Cu—Sn alloy coating layer and the base material.

As surface-roughening methods, JP-B-3926355 and JP-B-4024244 mentionphysical methods such as ion etching, chemical methods such as etchingand electrolytic polishing, and mechanical methods such as rolling(using a work roll with a surface roughened by polishing, shot-blasting,etc.), polishing, and shot-blasting. It is also mentioned that rollingand polishing are preferred as methods that are advantageous inproductivity, economical efficiency, and the surface configurationreproducibility of the base material. When the base material issurface-roughened by rolling, rolling is performed using a work rollwith a roughened surface to transfer the surface configuration of thework roll. However, in reality, by such a method, it was difficult toachieve the surface roughness specified by the present invention becauseof the following reasons. In the case of rolling, for example, in orderto form deep depressions and projections uniformly over the entiresurface of the work roll surface at fine intervals, high cost isrequired. There also are problems of abrasion of the roll, clogging, andthe like. Accordingly, it is difficult to transfer thedepression-projection shape corresponding to the surface roughnessspecified by the present invention (deep grooves formed at fineintervals) uniformly onto the entire surface of the copper sheet.

Meanwhile, JP-A-2008-269999 and JP-A-2008-274364 describe a technique ofperforming surface roughening at the time of the formation of a terminalshape. That is, a copper sheet is stamped to form a copper sheetincluding terminal pieces connected in chains in the lengthwisedirection via strip-like connecting portions. Also, at the same time asstamping or at an earlier or later time, the copper sheet is pressed toincrease the surface roughness of the terminal piece plate surface(surface of the copper sheet). JP-A-2008-269999 or JP-A-2008-274364nowhere describes a specific pressing process. However, for example, asshown in FIG. 4, a die 1 having extremely fine depressions andprojections formed on the pressing surface thereof with constant pitchis mounted on a pressing machine, and then the surface of a copper sheet2 is pressed with the die 1 so that the depression-projection shape ofthe pressing surface is transferred onto the surface of the copper sheet2 (projections (blade edges) cut deeply thereinto); in this manner, thesurface of the copper sheet can be provided with the surface roughnessspecified by the present invention. The method for forming finedepressions and projections on the pressing surface of the die 1 may beelectrical discharging, grinding, laser processing, or the like, and anyof them can be selected according to the desired dimensional accuracyand processing shape.

When the projections on the pressing surface of the die are formed inthe form of parallel lines, for example, fine grooves (valleys of aroughness curve) can be formed in the form of parallel lines deep in thesurface of the copper sheet by the surface-roughening method. Further,as described below in the Example, grooves may also be formed in a gridpattern where grooves in the form of parallel lines cross each other.Upon ref lowing, molten Sn flows into the grooves and solidifies to forma Sn coating layer in the form of parallel lines as shown in FIG. 6.When grooves are formed in the form of parallel lines by surfaceroughening in this manner, it is preferable that the direction ofgrooves does not match the direction of terminal insertion (thedirection of grooves and the direction of terminal insertion cross eachother). In the case where such grooves are formed in the surface of thecopper sheet, the arithmetic mean roughness Ra of the copper sheetincreases when the measurement direction and the grooves cross eachother. The mean roughness Ra does not greatly change with the crossingangle.

Hereinafter, the mating-type connecting part according to the presentinvention will be described in detail.

The mating-type connecting part according to the present invention isobtained by post-plating and ref lowing a copper sheet stamped into apredetermined shape and includes a mixture of a Cu—Sn alloy coatinglayer and a Sn coating layer on an outermost surface thereof on the sidethat is contact with a mating part. The Sn coating layer is smoothed byref lowing. More specifically, the surface coating layer formed of theCu—Sn alloy coating layer and the Sn coating layer is configured suchthat the Cu—Sn alloy coating layer and the Sn coating layer are formedin this order on the surface of a copper sheet (base material), and aportion of the Cu—Sn alloy coating layer is exposed on the outermostsurface through the Sn coating layer smoothed by reflowing. When thehard Cu—Sn alloy coating layer is exposed on the outermost surface onthe side that is contact with a mating part (sliding side), the terminalinsertion force is reduced.

The Cu—Sn alloy coating layer exposed on the outermost surface ismeasured as a peak of a roughness curve according to JIS B0601, and sucha peak is reflected by the magnitude of maximum height roughness Rz.

In the mating-type connecting part according to the present invention,the Sn coating layer and the Cu—Sn alloy coating layer present on theoutermost surface on the side that is contact with a mating part areconfigured as the following (1) or (2):

(1) a Sn coating layer group observed as a plurality of parallel linesis included, and the Cu—Sn alloy coating layer is present adjacent toeach side of each of Sn coating layers constituting the Sn coating layergroup (these Sn coating layers are sometimes particularly referred to asparallel Sn coating layers); or

(2) a Sn coating layer group observed as a plurality of parallel linesand one or more additional Sn coating layer groups each observed as aplurality of parallel lines are included, the Sn coating layer groupscross each other in a grid pattern, and the Cu—Sn alloy coating layer ispresent adjacent to each side of each of Sn coating layers constitutingeach Sn coating layer group (these Sn coating layers are sometimesparticularly referred to as parallel Sn coating layers).

The configurations (1) and (2) of the parallel Sn coating layers and theCu—Sn alloy coating layer will be described with reference to theschematic diagrams of FIGS. 8A, 8B, 9A, and 9B. FIGS. 8A, 8B, 9A, and 9Beach show a schematic plan view of a portion of the outermost surface ofa mating-type connecting part taken in a substantially square shape.

First, FIGS. 8A and 8B show typical examples of the configuration (1).In the example shown in FIG. 8A, a plurality of parallel Sn coatinglayers 101 a to 101 d (sometimes collectively referred to as parallel Sncoating layers 101) having a predetermined width are formed in the formof parallel lines at substantially regular intervals, and a Cu—Sn alloycoating layer 102 is present adjacent to each side of each of theparallel Sn coating layers 101 a to 101 d. The Cu—Sn alloy coating layer102 has a predetermined width and is also formed in the form of parallellines at substantially regular intervals. The plurality of parallel Sncoating layers 101 a to 101 d formed in the form of parallel linesconstitute a Sn coating layer group X as defined herein.

In the example shown in FIG. 8B, a plurality of parallel Sn coatinglayers 101 a to 101 d having a predetermined width are formed in theform of parallel lines at substantially regular intervals, and a Cu—Snalloy coating layer 102 is present adjacent to each side thereof.Although the Cu—Sn alloy coating layer 102 has a predetermined width andis also formed in the form of parallel lines at substantially regularintervals, this example is different from the example of FIG. 8A in thata Sn coating layer 103 is present in the form of islands in the Cu—Snalloy coating layer 102. The plurality of parallel Sn coating layers 101formed in the form of parallel lines constitute a Sn coating layer groupX as defined herein.

In FIG. 8B, various other configurations are possible. For example, theSn coating layers 103 in the form of island may be continuous to dividethe Cu—Sn alloy coating layer 102, or a further Cu—Sn alloy coatinglayers may be present in the form of small islands in the Sn coatinglayer 103.

FIGS. 9A and 9B show typical examples of the configuration (2). In theexample shown in FIG. 9A, a plurality of parallel Sn coating layers 101a to 101 d having a predetermined width are formed in the form ofparallel lines at substantially regular intervals. Further, at rightangles thereto, a plurality of parallel Sn coating layers 104 a to 104 d(sometimes collectively referred to as parallel Sn coating layers 104)having a predetermined width are formed in the form of parallel lines atsubstantially regular intervals. The plurality of parallel Sn coatinglayers 101 a to 101 d formed in the form of parallel lines constitute aSn coating layer group X as defined herein, and the plurality ofparallel Sn coating layers 104 a to 104 d formed in the form of parallellines constitute a Sn coating layer group Y as defined herein. The twoSn coating layer groups X and Y cross each other in a grid pattern, andthe Cu—Sn alloy coating layer 102 is present in each area defined by thegrid. Also in this case, it can be said that the Cu—Sn alloy coatinglayer 102 is present adjacent to each side of each of the parallel Sncoating layers 101 and 104.

In the example shown in FIG. 9b , a plurality of parallel Sn coatinglayers 101 a to 101 d having a predetermined width are formed in theform of parallel lines at substantially regular intervals. Further, atright angles thereto, a plurality of parallel Sn coating layers 104 a to104 d having a predetermined width are formed in the form of parallellines at substantially regular intervals. The plurality of parallel Sncoating layers 101 a to 101 d formed in the form of parallel linesconstitute a Sn coating layer group X as defined herein, and theplurality of parallel Sn coating layers 104 a to 104 d formed in theform of parallel lines constitute a Sn coating layer group Y as definedherein. The two Sn coating layer groups X and Y cross each other in agrid pattern, and the Cu—Sn alloy coating layer 102 is present in eacharea defined by the grid. This example is different from the example ofFIG. 9A in that a Sn coating layer 103 is present in the form of islandsin the Cu—Sn alloy coating layer 102. Also in this case, it can be saidthat the Cu—Sn alloy coating layer 102 is present adjacent to each sideof each of the parallel Sn coating layers 101 and 104.

In addition, various other configurations are possible. For example, inFIG. 9B, a further Cu—Sn alloy coating layer may be present in the formof small islands in the Sn coating layer 103 formed in islands.

In the mating-type connecting part shown in FIG. 8A, 8B, 9A, or 9B, theCu—Sn alloy coating layer 102 exposed on the surface protrudes in theheight direction from the level of the parallel Sn coating layers 101(as well as the Sn coating layer 103 and the parallel Sn coating layers104) smoothed by ref lowing. Cross-sectional configurations of suchcoating layers will be described with reference to the schematiccross-sectional views of FIGS. 10A and 10B.

In FIGS. 10A and 10B, relatively deep depressions 106 are formed in thecopper sheet (base material) 105 at substantially regular intervals, anda projection 107 is formed on each side of each depression 106. Theregion between adjacent projections 107,107 with no depression 106therebetween is relatively flat. Such a surface structure is called aplateau structure. The depressions 106 are observed as a plurality ofparallel lines in the surface of the copper sheet 105.

FIG. 10A corresponds to FIG. 8A (or FIG. 9A). A Cu—Sn alloy coatinglayer 102 is formed over the entire surface of the copper sheet 105. Inthe depressions 106, parallel Sn coating layers 101 are formed on theCu—Sn alloy coating layer 102. The parallel Sn coating layers 101 formedin the depressions 106 are equivalent to the parallel Sn coating layers101 a to 101 d (or the parallel Sn coating layers 104 a to 104 d)observed in the form of parallel lines in FIG. 8A or FIG. 9A.

FIG. 10B corresponds to FIG. 8B (or FIG. 9B). A Cu—Sn alloy coatinglayer 102 is formed over the entire surface of the copper sheet 105. Inthe depressions 106, parallel Sn coating layers 101 are formed on theCu—Sn alloy coating layer 102. Also in a plateau region, a Sn coatinglayer 103 is formed on the Cu—Sn alloy coating layer 102. The parallelSn coating layers 101 formed in the depressions 106 are equivalent tothe parallel Sn coating layers 101 a to 101 d (or the parallel Sncoating layers 104 a to 104 d) observed in the form of parallel lines inFIG. 8B or FIG. 9B, and the Sn coating layer 103 formed in the plateauregion is equivalent to the Sn coating layer 103 observed in the form ofislands in FIG. 8B or FIG. 9B.

With respect to the configuration of the surface coating layer includingthe Cu—Sn alloy coating layer 102 and the parallel Sn coating layers 101(and the parallel Sn coating layers 104), a specific example of itsformation process will be described.

After, before, or at the same time as stamping into a part shape, thecopper sheet 105 is subjected to a surface-roughening process bypressing. The surface roughening process is performed as follows. Asshown in FIG. 11A, a die 108 with extremely fine depressions andprojections formed on the pressing surface thereof at approximatelyconstant pitch is mounted on a pressing machine, and the die 108 ispressed against the surface of the copper sheet 105. By such pressing,the projections (blade edges) on the pressing surface of the die 108 arepressed into the surface of the copper sheet 105, and the shape of thedepressions 106 is transferred to the surface of the copper sheet 105 inthe form of parallel lines. At the same time, the material pushed out bythe depressions 106 rises on both sides of each depression 106,naturally forming projections 107. With respect to the copper sheetsurface between the adjacent projections 107,107 with no depression 106therebetween, the region remains relatively flat (plateau) as shaped byfinish rolling.

Subsequently, in the same manner as in JP-B-3926355, JP-B-4024244 andJP-A-2007-258156, etc., the surface of the copper sheet 105 stamped intoa part shape is plated with Cu and Sn, for example, and then is furthersubjected to a ref lowing process. By the ref lowing process, a Cu—Snalloy coating layer is formed from Cu of the Cu plating layer and Sn ofthe Sn plating layer, and molten Sn flows into the depressions 106, etc.As a result, as shown in FIG. 10A, smoothed parallel Sn coating layers101 are formed on the Cu—Sn alloy coating layer 102, and portions of theCu—Sn alloy coating layer 102 are exposed adjacent to the parallel Sncoating layers 101 on both sides of the parallel Sn coating layers 101.At this time, a portion of the Cu plating layer may remain under theCu—Sn alloy coating layer 102.

As used herein, a “coating layer” refers to each of the layersconstituting a surface coating layer after ref lowing, while a “platinglayer” refers to each of the layers constituting a surface plating layerbefore ref lowing.

When the amount of Sn remaining after ref lowing is relatively large,the Sn coating layer 103 is formed on a part of the plateau region ofthe copper alloy plate surface (see FIG. 8B, FIG. 9B, and FIG. 10B) orthe area covered with the Sn coating layer 103 is increased. As shown inFIG. 10B, the Sn coating layer 103 is thinner than the parallel Sncoating layers 101.

The parallel Sn coating layers 101 constituting the Sn coating layergroup X and the parallel Sn coating layers 104 constituting the Sncoating layer group Y are configured such that the widths a and b (seeFIGS. 8A, 8B, 9A, and 9B) are each 1 to 500 μm, and the intervals c andd between adjacent parallel Sn coating layers (see FIGS. 8A, 8B, 9A, and9B) are each 1 to 2000 μm. The reason why the width of each parallel Sncoating layer and the interval between adjacent parallel Sn coatinglayers should be as above is that within the ranges, the parallel Sncoating layers and the Cu—Sn alloy coating layer are moderately mixed onthe outermost surface, whereby both reduced insertion force due to a lowfriction coefficient and electrical reliability can be ensured.

More specifically, the reason why the parallel Sn coating layers shouldhave a width of 1 μm or more is that when the parallel Sn coating layershave a smaller width, this makes it difficult to perform surfaceroughening process of the copper sheet. Meanwhile, when the width of theparallel Sn coating layers is too large, the contact portion of themating terminal breaks into the parallel Sn coating layers, therebyincreasing insertion force. Therefore, the parallel Sn coating layersshould have a width of 500 μm or less. In light of the recentminiaturization of terminals, the parallel Sn coating layers preferablyhave a width of 200 μl or less, and more preferably 50 μm or less.

The reason why the interval between adjacent parallel Sn coating layersshould be 1 μm or more is that this makes it difficult to performsurface roughening of the copper sheet. Meanwhile, when the intervalbetween adjacent parallel Sn coating layers is too large, depending onthe initial Sn plating layer thickness, the area of contact between themating terminal and the Cu—Sn alloy coating layer is likely to be toolarge or too small, thereby causing an increase in insertion force(decrease in insertion-force-reducing effect) in any case. Therefore,the interval between adjacent parallel Sn coating layers should be 2000μm or less. In light of the recent miniaturization of terminals, theparallel Sn coating layers preferably have a width of 1000 μm or less,and more preferably 250 μm or less. It is preferable that the width ofthe parallel Sn coating layers and the interval of adjacent parallel Sncoating layers are substantially constant, but this is not essential.

As shown in FIGS. 10A and 10B, the Cu—Sn alloy coating layer 102 exposedon the outermost surface protrudes in the height direction from thelevel of the parallel Sn coating layers 101 and the Sn coating layer103. Therefore, when the surface roughness is measured in the directionof terminal insertion (indicated by a white arrow in FIGS. 8A, 8B, 9A,and 9B), for example, the Cu—Sn alloy coating layer 102 is measured aspeaks of a roughness curve according to JIS B0601.

The present invention specifies the maximum height roughness Rz to be 10μm or less (including 0 μm) in the direction of part (terminal)insertion. When the maximum height roughness Rz is larger, the surfacearea of the Cu—Sn alloy coating layer exposed on the outermost surfaceincreases, and the corrosion resistance of the part surface decreases toincrease the oxide amount, etc. The contact resistance is thus likely toincrease, making it difficult to maintain electrical reliability.Further, when the depression 106 formed by surface-roughening the coppersheet is wide and deep in the copper sheet 105, its maximum heightroughness Rz is large, but this is likely to cause deformation of thecopper sheet 105. Therefore, the maximum height roughness Rz is 10 μm orless, and preferably more than 0 (somewhat protruding) to not more than5 μm.

In the examples shown in FIGS. 9A and 9B, the two parallel Sn coatinglayer groups X and Y cross each other at right angles. However, thecrossing angle can be suitably adjusted. When the two parallel Sncoating layer groups X and Y cross each other, the corner portions ofthe Cu—Sn alloy coating layer rise even higher (a corner at the positionwhere two depressions cross each other in surface roughening rises),thereby increasing the insertion-force-reducing effect. However, whenthe width of the parallel Sn coating layers and the interval betweenadjacent parallel Sn coating layers are the same, the smaller thecrossing angle, the wider the interval between the rises, therebydecreasing the insertion-force-reducing effect. Therefore, the crossingangle is preferably 10° to 90°.

The present invention also encompasses the case where three or more Sncoating layer groups cross one another in a grid pattern. Also in thiscase, the Sn coating layers of each Sn coating layer group have a widthof 1 to 500 μm, and the interval between adjacent parallel Sn coatinglayers in one Sn coating layer Sn coating layer group is 1 to 2000 μm.The crossing angles of the Sn coating layer groups are also eachpreferably 10 to 90°.

In the mating-type connecting part according to the present invention,the angle defined by the part (terminal) insertion direction and thelengthwise direction of the Sn coating layer group should be suitablyadjusted within a range of 0° to 90°. When the number of Sn coatinglayer groups is one, the angle is preferably more than 0° to 90°. Alarger angle is more preferred, and the angle is more preferably 20° to90°, and further preferably 90°. When the number of Sn coating layergroups is two or more, at least one Sn coating layer group is set tomake the above angle with the insertion direction.

In the surface coating layer formed on the surface of the copper sheet,the Cu—Sn alloy coating layer is made of either or both of Cu6Sn5 andCu3Sn and has an average thickness of 0.1 to 3.0 μm. This is on the samelevel as those of related art (JP-B-3926355 and JP-B-4024244). When theaverage thickness of the Cu—Sn alloy coating layer is less than 0.1 μm,the corrosion resistance of the material surface decreases to increasethe oxide amount, etc. The contact resistance is thus likely toincrease, making it difficult to maintain electrical reliability.Meanwhile, when the average thickness is more than 3.0 μm, this isdisadvantageous in terms of cost, and productivity is also reduced.Therefore, the Cu—Sn alloy coating layer should have an averagethickness of 0.1 to 3.0 μm, and more preferably 0.2 to 1.0 μm.

The Sn coating layer is made of a Sn metal or a Sn alloy. In the case ofa Sn alloy, alloy elements may be Cu, Ag, Ni, Bi, Zn, and the like.These elements are preferably 10 mass % or less. The Sn coating layershould have an average thickness of 0.2 to 5.0 μm. This is on the samelevel as those of related art (JP-B-3926355 and JP-B-4024244). When theaverage thickness of the Sn coating layer is less than 0.2 μm, thisresults in an increased amount of Cu oxide on the material surface dueto thermal diffusion by high-temperature oxidation, etc. This is likelyto cause an increase in contact resistance and a decrease in corrosionresistance, thereby making it difficult to maintain electricalreliability. Meanwhile, when the average thickness is more than 5.0 μm,this is disadvantageous in terms of cost, and productivity is alsoreduced. Therefore, the Sn coating layer should have an averagethickness of 0.2 to 5.0 μm, and more preferably 0.5 to 3.0 μm.

As a part of the surface coating layer of the mating-type connectingpart, a Ni coating layer may be formed between the surface of the coppersheet and the Cu—Sn alloy coating layer, and a Cu coating layer may befurther formed between the Ni coating layer and the Cu—Sn alloy coatinglayer. A Cu coating layer may further be formed between the surface ofthe copper sheet for connecting parts and the Ni coating layer. Thesecoating layers are all formed by plating. The Cu coating layer betweenthe Ni coating layer and the Cu—Sn alloy coating layer is a Cu platinglayer remaining under the Cu—Sn alloy coating layer after ref lowing asmentioned above.

The Ni coating layer is made of metal Ni or a Ni alloy. In the case of aNi alloy, alloy elements may be Cu, P, Co, and the like. Cu ispreferably 40 mass % or less, and P and Co are preferably 10 mass % orless. The Ni coating layer preferably has an average thickness of 0.1 to10 μm. The Cu coating layer is made of metal Cu or a Cu alloy. In thecase of a Cu alloy, alloy elements may be Sn, Zn, and the like. Sn ispreferably less than 50 mass %, and other elements are preferably 5 mass% or less. The Cu coating layer preferably has an average thickness of3.0 μm or less.

The following provides a supplementary explanation of the method forproducing the mating-type connecting part.

As surface-roughening methods, JP-B-3926355, JP-B-4024244 andJP-A-2007-258156 disclose physical methods such as ion etching, chemicalmethods such as etching and electrolytic polishing, and mechanicalmethods such as rolling (using a work roll with a surface roughened bypolishing, shot-blasting, etc.), polishing, and shot-blasting. However,such a method does not allow the formation of a Sn coating layer groupobserved as a plurality of parallel lines and a Cu—Sn alloy coatinglayer adjacent to each side thereof as mentioned above.

Meanwhile, JP-A-2008-269999 and JP-A-2008-274364 describe a technique ofroughening the surface of a cupper sheet at the time of the formation ofa terminal shape. That is, a copper sheet is stamped to form a coppersheet including terminal pieces connected in chains in the lengthwisedirection via strip-like connecting portions. Also, at the same time asstamping or at an earlier or later time, the copper sheet is pressed toincrease the surface roughness of the terminal piece plate surface(surface of the copper sheet). However, JP-A-2008-269999 orJP-A-2008-274364 nowhere describes a specific pressing process.

A Cu—Sn alloy coating layer is exposed in the area of projections on thesurface of the surface-roughened copper sheet (depressions andprojections are artificially formed) after ref lowing. Therefore, theexposure of the Cu—Sn alloy coating layer or the Sn coating layerreflects the configuration of depressions and projections formed on thesurface of the copper sheet during surface roughening.

In the present invention, the method for surface roughening may be suchthat, as described above with reference to FIGS. 11A and 11B, a diewith, on the pressing surface thereof, extremely fine depressions andprojections formed in the form of parallel lines is mounted on apressing machine, then the die is pressed against the surface of thecopper sheet to press the projections (blade edges) into the surface ofthe copper sheet. This method allows the Cu—Sn alloy coating layer orthe Sn coating layer to be exposed as specified by the presentinvention, and, in addition, the width of a Sn coating layer and theinterval between Sn coating layers can be freely controlled.

The method for forming fine depressions and projections on the pressingsurface of the die 108 may be electrical discharging, grinding, laserprocessing, or the like, and any of them can be selected according tothe desired dimensional accuracy and processing shape. The projectionshape and the formation pitch do not have to be constant.

After the copper sheet is stamped into a part shape andsurface-roughened, the copper sheet is subjected to so-calledpost-plating. In the copper sheet, the region to be surface-treated andpost-plated may entirely cover one or both surfaces of the copper sheetor may occupy only a portion of one or both surfaces. The treatmentsshould be applied at least to the surface that serves as a slidingsurface when the copper sheet is mated with the mating part.

Post-plating can be performed as follows. After performing Ni plating asrequired, a Cu plating layer and a Sn plating layer are formed in thisorder, and then ref lowed to give post-plating. If necessary, it is alsopossible to form a Cu plating layer under the Ni plating layer forimproving the adhesion of Ni plating. It is also possible that only a Snplating layer is directly formed on the surface of the copper sheet.

When the post-plated copper sheet is ref lowed, a Cu—Sn alloy coatinglayer is formed by the interdiffusion of Cu and Sn of the Cu platinglayer and the Sn plating layer. At that time, the Sn plating layerremains, while the Cu plating layer may entirely disappear or partiallyremain. When the Cu plating layer partially remains, a Cu coating layeris formed between the surface of the copper sheet (in the case where aNi layer is formed, the surface of the Ni layer) and the Cu—Sn alloycoating layer. In the case where a Ni layer is not formed, depending onthe thickness of the Cu plating layer, Cu may also be supplied from thecopper sheet (base material). When only a Sn plating layer is directlyformed on the surface of the copper sheet, Cu in the copper sheet (basematerial) and Sn in the Sn plating layer undergo interdiffusion, therebyforming a Cu—Sn alloy coating layer.

The Cu plating layer preferably has an average thickness of 0.1 to 1.5μm, the Sn plating layer preferably has an average thickness of 0.3 to8.0 μm, and the Ni plating layer preferably has an average thickness of0.1 to 10 μm.

In the present invention, the Cu plating layer, the Sn plating layer,and the Ni plating layer contain a Cu alloy, a Sn alloy, and a Ni alloy,respectively, in addition to the Cu, Sn, and Ni metals. When the Cuplating layer, the Sn plating layer, and the Ni plating layer are a Cualloy, a Sn alloy, and a Ni alloy, the alloy elements of such alloys maybe the same as in the alloys of the Cu coating layer, the Sn coatinglayer, and the Ni coating layer, respectively.

Hereinafter, main points of the present invention will be described infurther detail with reference to Examples. However, the presentinvention is not limited to these Examples.

Example 1 Production of Cu Alloy Base Material

In this example, a copper alloy strip containing Ni, Si, Zn, and Sn inamounts of 1.8 mass %, 0.40 mass %, 1.1 mass %, and 0.10 mass % based onCu, respectively, and having a Vickers hardness of 180 and a thicknessof 0.25 mmt was produced.

A specimen with a size of 100 mm×40 mm (rolling/longitudinaldirection×perpendicular direction) was cut from the copper alloy strip.A part provided with predetermined depressions and projections on thepressing surface thereof was mounted at a predetermined position in aprogressive die for forming pin terminals (position after the formationof the pin terminals), and pin terminal shapes with a size of 1 mm w×22mm L were formed with a pitch of 5 mm. At the same time, a 1 mm w×10 mmL area of the surface of each pin terminal was surface-roughened. FIG. 5shows a schematic diagram of the copper sheet after the formation andthe surface roughening. In FIG. 5, 2 is the copper sheet, 3 is the pinterminal area, and the two direction arrow indicates thesurface-roughened portion. By using parts with depressions andprojections of different shapes, for example, various surfaceroughnesses can be obtained.

However, with respect to No. 11, which is a related-art material,following JP-B-3926355 and JP-B-4024244, the copper sheet was entirelysurface-roughened by rolling with a work roll having a roughenedsurface, and the copper sheet was then formed into a pin terminal shape.With respect to No. 12, which also is a related-art material, no surfaceroughening was performed.

Subsequently, the surface roughness was measured by the followingmethods. The measured arithmetic mean roughness Ra, meanprojection-depression interval RSm, Skewness Rsk, and protrusion peakportion height Rpk are shown in Table 1. The roughness curve, amplitudecurve, and load curve of No. 1 are shown in FIGS. 1 to 3.

Method for Measurement of Surface Roughness

Using a contact roughness meter (TOKYO SEIMITSU CO, LTD; SURFCOM 1400),surface roughness was measured according to JIS B0601:2001 and JISB0671:2002. The conditions for the measurement of surface roughness wereas follows. With a cutoff value of 0.8 mm, a reference length of 0.8 mm,an evaluation length of 4.0 mm, a measurement rate of 0.3 mm/s, and acontact needle tip radius of 5 μmR, measurements were made at severalpoints along the direction of pin terminal insertion. Based on theroughness curve that provided the maximum arithmetic mean roughness Ra,each surface roughness parameter was determined. Further, with respectto test materials Nos. 1 to 10 and 13 to 17, the arithmetic meanroughness Ra was measured also in other directions than the pin terminalinsertion direction within the range ensuring an evaluation length of4.0 mm. As a result, in these specimens, in every direction, thearithmetic mean roughness Ra was nearly the same as or less than themaximum of the arithmetic mean roughness Ra measured in the pin terminalinsertion direction.

Subsequently, copper sheets Nos. 1 to 17 were plated with Cu and Sn, andthen ref lowed at 280° C. for 10 sec to give specimens. The Cu platinglayer was formed to have an average thickness of 0.15 μm. The Sn platinglayer was formed to have a varying average thickness of 0.7 μm, 1.0 μm,and 1.3 μm, so that the Sn coating layer after ref lowing had athickness of 0.4 μm, 0.7 μm, and 1.0 μm, respectively.

FIG. 6 shows the surface SEM (composition image) of Example 1 (thicknessof Sn coating layer: 0.7 μm). In the figure, the white zone is the Sncoating layer, and the black zone is the Cu—Sn alloy coating layer,showing that the Cu—Sn alloy coating layer and the Sn coating layer areformed on the outermost surface (the Cu—Sn alloy coating layer isexposed through the Sn coating layer). In this example, Sn coatinglayers in the form of parallel lines cross each other at right angles ina grid pattern. The direction of each Sn coating layer is set at anangle of 45° relative to the terminal insertion direction. Also in Nos.2 to 10 and 13 to 17, Sn coating layers in the form of parallel lines(including Sn coating layers in a grid pattern) are formed.

The average thicknesses of the Cu plating layer, the Sn plating layer,and the Sn coating layer are measured as follows.

Method for Measurement of Cu Plating Layer Average Thickness

A cross section of a test material processed by the microtome methodbefore ref lowing was observed using SEM (scanning electron microscope)at a magnification of 10,000×, and the average thickness of Cu platingwas calculated by image analysis processing.

Method for Measurement of Sn Plating Layer Average Thickness

Using a fluorescent X-ray thickness gauge (Seiko Instruments Inc.,SFT3200), the average thickness of Sn plating of a test material beforeref lowing was calculated. The measurement conditions were such that amonolayer calibration curve of Sn/base material was used as thecalibration curve, and the collimator diameter was set at φ0.5 mm.

Method for Measurement of Sn Coating Layer Average Thickness

First, using a fluorescent X-ray thickness gauge (Seiko InstrumentsInc., SFT3200), a test material was measured for the sum of thethickness of the Sn coating layer and the thickness of the Sn componentcontained in the Cu—Sn alloy coating layer. Subsequently, each testmaterial was immersed in an aqueous solution of p-nitrophenol andcaustic soda for 10 minutes to remove the Sn coating layer. Thethickness of the Sn component contained in the Cu—Sn alloy coating layerwas measured again using a fluorescent X-ray thickness gauge. Themeasurement conditions were such that a monolayer calibration curve ofSn/base material was used as the calibration curve, and the collimatordiameter was set at φ0.5 mm. The measurement of the sum of the thicknessof the Sn coating layer and the thickness of the Sn component containedin the Cu—Sn alloy coating layer was performed as follows. In the caseof a 1-mm-wide specimen, measurement points were taken at the centerposition of a specimen in the width direction thereof (directionperpendicular to the longitudinal direction) and two positions acrossthe center position where the end of an X-ray from a collimator is notapplied to sags at the corner portions formed by stamping (threepositions in total). In the case of a 3-mm-wide stamped material,measurement points were taken at the center position of a specimen inthe width direction thereof (direction perpendicular to the longitudinaldirection) and the positions 0.5 mm from the both ends (three positionsin total). In each position, a point was taken at the position 1 mm fromthe lengthwise end, and points were also taken with a pitch of 0.5 mmfrom such a position along the longitudinal direction; ten points wereselected in total. Thus, for each specimen, measurements were made atthree positions×ten points (30 points in total), and the average thereofwas calculated. The thickness of the Sn component contained in the Cu—Snalloy coating layer was also measured in the same manner. The thicknessof the Sn component contained in the Cu—Sn alloy coating layer wassubtracted from the sum of the thickness of the Sn coating layer and thethickness of the Sn component contained in the Cu—Sn alloy coatinglayer, thereby calculating the average thickness of the Sn coatinglayer.

Subsequently, the obtained specimens were subjected to a frictioncoefficient evaluation test in the following manner. The results areshown in Table 1. In Table 1, regarding friction coefficient, theemboss-1.5 columns show friction coefficients where the inner diameterof the hemisphere of a female specimen is 1.5 mm, while the emboss-1.0columns show friction coefficients where the inner diameter of thehemisphere of a female specimen is 1.0 mm.

Friction Coefficient Evaluation Test

The shape of an indented portion of an electrical contact in amating-type connecting part was imitated, and the evaluation wasperformed using an apparatus as shown in FIG. 7. First, a male specimen4 in the shape of a pin terminal cut from each test material (Nos. 1 to17) was fixed on a horizontal platform 5, and a female specimen 6 wasplaced thereon to bring coating layers into contact with each other. Thefemale specimen 6 is a processed hemisphere material (inner diameter:φ1.5 mm and φ1.0 mm) cut from a material obtained, using the basematerial No. 12, by plating a flat plate not formed into a terminal (Cu:0.15 μm, Sn: 1.0 μm, ref lowed). Subsequently, a load of 3.0 N (spindle7) was applied to the female specimen 6 to press the male specimen 4,and, using a horizontal load measuring device (AIKOH ENGINEERING CO,LTD.; Model-2152), the male specimen 4 was pulled in the directionhorizontal to the terminal insertion direction (sliding rate: 80 mm/min)to measure the maximum frictional force F until a sliding distance of 5mm (unit: N). The friction coefficient was determined by the followingformula (1). The reference numeral 8 is a load cell, and the arrow isthe sliding direction.Friction coefficient=F/3.0:  (1))

TABLE 1 Sn Coating Surface Roughness Layer Friction Coefficient Ra RSmRpk Thickness Emboss Emboss No. (μm) (mm) Rsk (μm) (μm) 1.5 1.0 1 1.870.08 −0.76 0.32 0.4 0.28 0.31 0.7 0.30 0.38 1.0 0.34  0.52 * 2 1.47 0.09−1.01 0.40 0.4 0.28 0.29 0.7 0.35 0.36 1.0 0.36  0.50 * 3 0.96 0.08−1.50 0.39 0.4 0.32 0.30 0.7 0.39 0.39 1.0 0.39  0.49 * 4 0.60 0.08−1.70 0.32 0.4 0.31 0.33 0.7 0.35 0.38 1.0 0.39  0.54 * 5 1.20 0.04−1.23 0.31 0.4 0.35 0.33 0.7 0.38 0.36 1.0 0.39 0.39 6 3.4  0.29 −0.080.89 0.4 0.26 0.32 0.7 0.33  0.55 * 7 3.8  0.11 −0.02 0.96 0.4 0.26 0.320.7 0.29 0.35 1.0 0.32  0.50 * 8  0.32 * 0.08 −1.82 0.15 0.4 0.35 0.390.7  0.42 *  0.53 * 9  0.32 *  0.32 * −2.63 0.11 0.4  0.41 *  0.53 * 0.7 0.53 *  0.58 * 10 1.67  0.75 * −2.25 0.21 0.4  0.55 *  0.58 * 0.7 0.56 *  0.60 * 11 0.61 0.16    0.51 *  1.10 * 0.4 0.36  0.53 * 0.7 0.40 *  0.58 * 12  0.04 * 0.02 −0.76 0.04 0.4  0.45 *  0.47 * 0.7 0.56 *  0.59 * 13 3.0  0.03 −0.06 0.83 0.4 0.25 0.27 0.7 0.30 0.32 1.00.35 0.37 14 1.24 0.08 −1.21 0.52 0.4 0.24 0.30 0.7 0.36 0.39 1.0 0.42 *  0.45 * 15 2.7  0.09 −0.08 0.05 0.4 0.33 0.38 0.7 0.36  0.42 *1.0 0.38  0.55 * 16 1.33 0.08 −1.25 0.25 0.4 0.33 0.39 0.7 0.35  0.43 *1.0 0.37  0.54 * * Outside the specified range or with inferiorcharacteristics

As shown in Table 1, Nos. 1 to 7 and 13 to 16 satisfy the requirementsspecified by the present invention in terms of surface roughness. In thecase of emboss 1.5, even when the thickness of the Sn coating layer is0.7 μm, the friction coefficient is less than 0.4, showing excellentcharacteristics.

Of these, Nos. 1 to 5, 7, 13 and 14 each have a protrusion peak portionheight Rpk within a range of 0.3 to 1 μm. Thus, on the peak portionsexpressed by the mean projection-depression interval RSm, there is aportion further protruding from the surface. Accordingly, even in thecase of emboss 1.0, when the thickness of the Sn coating layer is 0.7μm, the friction coefficient is as small as less than 0.4. No. 6 has amean projection-depression interval RSm as relatively large as 0.29 mm.In the case of emboss 1.0, when the Sn coating layer thickness is 0.7μm, the friction coefficient is as high as 0.55.

Meanwhile, No. 8 has an arithmetic mean roughness Ra of 0.32 μm and thushas small depressions and projections on the surface. Therefore, whenthe thickness of the Sn coating layer is 0.7 μm, the frictioncoefficient is large. No. 9 has a small arithmetic mean roughness Ra andalso has a large mean projection-depression interval RSm. Therefore,even when the thickness of the Sn coating layer is 0.4 μm, the frictioncoefficient is large. No. 10 has a large mean projection-depressioninterval RSm, so the friction coefficient is large. No. 11 is an exampleof related art. Although it satisfies the specified range in terms ofarithmetic mean roughness Ra and mean projection-depression intervalRSm, because the skewness Rsk is on the + side, even in the case ofemboss 1.5, when the thickness of the Sn coating layer is 0.7 μm, thefriction coefficient is large. No. 12 is another example of related art.It has a small arithmetic mean roughness Ra, so the friction coefficientis large.

Example 2

In addition to Nos. 4, 5, 7, 13, and 14 used in Example 1, No. 17 wasnewly formed, surface-roughened, plated, and ref lowed in the samemanner as in Example 1 to prepare specimens. Subsequently, the surfaceroughness (including protrusion valley portion depth Rvk), the thicknessof the Sn coating layer, and the friction coefficient were measured inthe same manner. Nos. 4 and 17, as well as Nos. 5 and 14, are similar toeach other in terms of arithmetic mean roughness Ra, meanprojection-depression interval RSm, skewness Rsk, and protrusion peakportion height Rpk, and are different from each other in terms ofprotrusion valley portion depth Rvk. Further, Nos. 4, 5, 7, 13, 14, and17 were measured for contact resistance after high-temperature storageas follows. The results are shown in Table 2.

Contact Resistance Evaluation Test after High-Temperature Storage

Each test material was heat-treated in air at 160° C. for 120 hours and500 hours, and then measured for contact resistance by a four-probemethod under the following conditions: open-circuit voltage, 20 mV;current, 10 mA; no sliding.

TABLE 2 Sn Heat Coating Friction Resistance Surface Roughness LayerCoefficient 160° C. Ra RSm Rpk Rvk Thickness Emboss 120 hr 500 hr No.(μm) (mm) Rsk (μm) (μm) (μm) 1.5 (mΩ) (mΩ) 4 0.60 0.08 −1.70 0.32 2.560.4 0.31 0.4 1.0 0.7 0.35 0.4 0.8 1.0 0.39 0.3 0.6 5 1.20 0.04 −1.230.31 3.23 0.4 0.35 0.7  1.2 * 0.7 0.38 0.5  1.1 * 1.0 0.39 0.4 0.7 7 3.80.11 −0.02 0.96 14    0.4 0.26 0.8  1.5 * 0.7 0.29 0.6  1.3 * 1.0 0.320.5 0.9 13 3.0 0.03 −0.06 0.83 5.5  0.4 0.25 0.7  2.1 * 0.7 0.30 0.5 1.3 * 1.0 0.35 0.4 0.8 14 1.24 0.08 −1.21 0.52  1.83 * 0.4 0.24 0.6 1.2 * 0.7 0.36 0.5 1.0 1.0  0.42 * 0.3 0.8 17 0.63 0.08 −1.82 0.25 1.33 * 0.4 0.33 0.6  1.1 * 0.7 0.39 0.5 1.0 1.0  0.55 * 0.3 0.7 *Outside the specified range or with inferior characteristics

As shown in Table 2, Nos. 4, 5, 7, 13, 14, and 17 all satisfy therequirements in terms of arithmetic mean roughness Ra, meanprojection-depression interval RSm, skewness Rsk, and protrusion peakportion height Rpk. Accordingly, when the thickness of the Sn coatinglayer is 0.7 μm, the friction coefficient is as small as less than 0.4.Of these, particularly Nos. 4, 5, 7, and 13 are within the specifiedrange in terms of protrusion valley portion depth Rvk, and even when thethickness of the Sn coating layer is 1.0 μm, the friction coefficient isas small as less than 0.4.

Meanwhile, Nos. 14 and 17 are outside the specified range in terms ofprotrusion valley portion depth Rvk, and when the thickness of the Sncoating layer is 1.0 μm, the friction coefficient is 0.4 or more. InNos. 14 and 15, in order to for the contact resistance to be less than1.0 mΩ after heating at 160° C. for 500 hours, it is necessary that theSn coating thickness is 1.0 μm or more. Accordingly, it is difficult toachieve both a low friction coefficient and high contact reliability.However, in Nos. 4, 5, 7, and 13 having Rvk within the specified range,the Sn coating thickness can be 1.0 μm, and it is possible to achieveboth a low friction coefficient and high contact reliability.

Example 3 Production of Copper Plate Material (Plated Base Material)

In this example, as in Example 1, a copper alloy strip containing Ni,Si, Zn, and Sn in amounts of 1.8 mass %, 0.40 mass %, 1.1 mass %, and0.10 mass based on Cu, respectively, and having a Vickers hardness of180 and a thickness of 0.25 mmt was produced.

A specimen with a size of 100 mm×40 mm (rolling/longitudinaldirection×perpendicular direction) was cut from the copper alloy strip.A part provided with predetermined depressions and projections on thepressing surface thereof was mounted at a predetermined position in aprogressive die for forming pin terminals (position after the formationof the pin terminals), and pin terminal shapes with a size of 1 mm w×22mm L were formed with a pitch of 5 mm. At the same time, a 1 mm w×10 mmL area of the surface of each pin terminal was surface-roughened. FIG.12 shows a schematic diagram of the copper sheet after the terminalformation and the surface roughening. In FIG. 12, 111 is the coppersheet, 112 is the pin terminal area, and the two direction arrowindicates the surface-roughened portion. By using parts with depressionsand projections of different shapes or by performing stamping severaltimes, for example, various surface configurations can be obtained.

Subsequently, the copper sheets Nos. 101 to 106 were plated with Ni(partially not plated) and then with Cu and Sn, and then ref lowed at280° C. for 10 sec to give specimens.

FIG. 13 shows the surface SEM (composition image) of No. 101. In thefigure, the white zone is the Sn coating layer, and the black zone isthe Cu—Sn alloy coating layer. The Sn coating layer includes two Sncoating layer groups each observed as a plurality of parallel lines, andone Sn coating layer group and the other Sn coating layer group crosseach other at an angle of 90°, making a grid pattern as a whole. In thisexample, after surface roughening and before plating, fine grooves(valleys) observed as a plurality of parallel lines are formed on thesurface of the pin terminal in such a manner that they cross one anotherat an angle of 90°, and such grooves form a grid pattern as a whole.

Table 3 shows the surface configuration and the average thickness ofeach coating layer of each specimen. In Table 3, the straight line Xindicates a Sn coating layer constituting one Sn coating layer group,and the straight line Y indicates a Sn coating layer constituting theother Sn coating layer group. When there is only one Sn coating layergroup, the straight line Y column is blank. With respect to eachspecimen, each parameter of the surface configuration and the averagethickness of each coating layer are measured as follows.

Maximum Height Roughness Rz

The measurement was performed using a contact roughness meter (TOKYOSEIMITSU CO, LTD; SURFCOM 1400) according to JIS B0601:2001. Theconditions for the measurement of surface roughness were as follows.With a cutoff value of 0.8 mm, a reference length of 0.8 mm, anevaluation length of 4.0 mm, a measurement rate of 0.3 mm/s, and acontact needle tip radius of 5 μmR, measurements were made at severalpoints along the direction of pin terminal insertion. The maximum heightroughness Rz was determined from each obtained roughness curve, and themaximum thereof was used as the maximum height roughness Rz of thespecimen. The values of maximum height roughness Rz were nearly the sameat all the measurement points. FIG. 13 shows an example of the roughnesscurve measured from No. 101.

Sn Layer Width and the Like

The surface of a specimen was observed using a scanning electronmicroscope, and, from its composition image, the Sn coating layer width(X, Y) and the intervals of the straight lines X and Y were measured.The crossing angle between X and Y and the crossing angle between X andthe insertion direction were adjusted in the stage of surfaceroughening.

Coating Layer Thickness

A specimen was cut along a cross section perpendicular to the Sn coatinglayers observed in the form of parallel lines, and the central part ofthe cross section was observed using a scanning electron microscope. Thecomposition image was subjected to image analysis processing tocalculate the average thicknesses of the Ni coating layer, the Cu—Snalloy coating layer, and the Sn coating layer. In all cases, the Cucoating layer had disappeared.

TABLE 3 Configuration of Surface Coating Layer Crossing Maximum AngleHeight Width of Straight Line Interval Crossing between X Thickness ofSurface Roughness Sn Coating Straight Straight Angle and InsertionCoating Layer Rz Layer X, Y Line X Line Y between X Direction Sn Cu—SnNi No. (μm) (μm) (μm) (μm) and Y (°) (°) (μm) (μm) (μm) 101 32 20  80 80 90 45 0.7 0.3 0.5 102 2.2 15  80  80 90 45 0.7 0.3 0.5 103 0.9 70 80  80 90 45 1.5 0.4 0.5 104 2.7 20  80 — — 90 0.7 0.3 0.5 105 2.3 25 80 — — 90 0.7 0.3 0.5 106 1.8  8  40 — — 90 0.7 0.3 1.0 107 8.3 15 300300 90 90 0.7 0.3 10.0  108 1.1 200  300 300 90 90 5.0 2.6 — 109 3.4 25750 750 90 90 0.7 0.3 — 110 <0.1 450  1000  1000  90 30 4.0 1.0 2.0 1110.2  1  3  3 10 90 0.2 0.1 0.1 112 5.3 100  300 300 60 60 0.7 0.3 0.5113 10.0 500  2000  2000  90 45 3.0 1.0 5.0 114 14.9* 300  1500  1500 90 30 0.7 0.3 — 115 5.1 700* 2000  — — 90 5.0 1.0 5.0 116 1.7 20 3000*3000* 90 90 0.7 0.3 0.5 *Outside the specified range

Subsequently, the obtained specimens were subjected to a frictioncoefficient evaluation test and a contact resistance evaluation testafter high-temperature storage in the following manner. The result isshown in Table 4. In Table 4, regarding friction coefficient, theemboss-1.5 columns show the friction coefficient where the innerdiameter of the hemisphere of a female specimen is 1.5 mm, while theemboss-1.0 columns show the friction coefficient where the innerdiameter of the hemisphere of a female specimen is 1.0 mm. The columnsfor tongue in Table 4 show friction coefficients in the case where thefemale specimen was a 10-mm-wide curved tongue (curvature radius: 2 mm).

Friction Coefficient Evaluation Test

The shape of an indented portion of an electrical contact in amating-type connecting part was imitated, and the evaluation wasperformed using an apparatus as shown in FIG. 14. First, a male specimen114 in the shape of a pin terminal cut from each test material (Nos. 101to 116) was fixed on a horizontal platform 115, and a female specimen116 was placed thereon to bring coating layers into contact with eachother. The female specimen 116 is a processed hemisphere material (innerdiameter: φ1.5 mm and φ1.0 mm) or a shaped tongue cut from a materialobtained by plating a not-surface-roughened copper sheet (Cu: 0.15 μm,Sn: 1.0 μm, ref lowed). Subsequently, a load of 3.0 N (spindle 117) wasapplied to the female specimen 106 to press the male specimen 114, and,using a horizontal load measuring device (AIKOH ENGINEERING CO, LTD;Model-2152), the male specimen 114 was pulled in the directionhorizontal to the terminal insertion direction (sliding rate: 80 mm/min)to measure the maximum frictional force F until a sliding distance of 5mm (unit: N). The friction coefficient was determined by the aboveformula (1). The reference numeral 118 is a load cell, and the arrow isthe sliding direction.

Contact Resistance Evaluation Test after High-Temperature Storage

Each test material was heat-treated in air at 160° C. for and 500 hours,and then measured for contact resistance by a four-probe method underthe following conditions: open-circuit voltage, 20 mV; current, 10 mA;no sliding. After heating at 160° C. for 500 hours, a specimen with acontact resistance of less than 1.0 mΩ was evaluated as having excellentheat resistance (◯), while one with a contact resistance of 1.0 mΩ ormore was evaluated as having poor heat resistance (x).

TABLE 4 Contact Friction Coefficient Resistance Emboss Emboss afterHeating No. 1.5 1.0 Tongue (mΩ) 101 0.30 0.38 ∘ 102 0.35 0.36 ∘ 103 0.390.53 * ∘ 104 0.39 0.39 ∘ 105 0.35 0.38 ∘ 106 0.38 0.36 ∘ 107 0.33 0.55 *∘ 108 0.37 0.45 * ∘ 109 0.56 * 0.60 * 0.39 ∘ 110 0.48 * 0.59 * 0.38 ∘111 0.33 0.37 0.36 ∘ 112 0.42 * 0.48 * 0.32 ∘ 113 0.55 * 0.57 * 0.31 ∘114 0.46 * 0.50 * 0.3 x 115 0.50 * 0.45 * 0.43 * ∘ 116 0.43 * 0.42 *0.45 * ∘ * With inferior properties

As shown in Table 4, Nos. 101 to 113 satisfy the requirements of thepresent invention in terms of the Sn coating layer width and interval,as well as maximum height roughness Rz. At least when the matingmaterial is a tongue, the friction coefficient is as low as 0.4. Inparticular, when the parameters are within a preferred range, that is,when the maximum height roughness Rz is 0.1 to 5 μm, the Sn coatinglayer width (lines X and Y) is 50 μm or less, and the interval betweenadjacent Sn coating layers (interval between adjacent lines X and X,interval between adjacent lines Y and Y) is 250 μm or less, even in thecase of emboss 1.0 mm, the friction coefficient is as small as less than0.4.

Meanwhile, in the case of No. 114, the maximum height roughness Rz istoo large, and thus the contact resistance after heating is high. In thecase of No. 115, the Sn coating layer width is too large, and thus thefriction coefficient is high. In the case of No. 116, the Sn coatinglayer intervals (interval between adjacent lines X and X, intervalsbetween adjacent lines Y and Y) is too large, and thus the frictioncoefficient is high.

What is claimed is:
 1. A method for producing a mating-type connectingpart, the method comprising: stamping a copper sheet into apredetermined shape, pressing a surface of the copper sheet with a diewhich has a plurality of parallel lines of projections formed on apressing surface of the die, thereby transferring the projections to thesurface of the copper sheet and forming depressions as the plurality ofparallel lines during, before, or after the stamping, plating thesurface of the depressions-made copper sheet with at least tin to form aSn coating layer, and reflowing the at least tin after the plating suchthat a surface of the Sn coating layer is smoothed and line-shaped Sncoating layers are each formed and exposed in each of the depressions ofthe copper sheet, and that a Cu—Sn alloy coating layer is formed andexposed adjacent to each side of each line-shaped Sn coating layer,wherein a maximum height roughness Rz of a surface of the mating-typeconnecting part on which the line-shaped Sn coating layers and the Cu—Snalloy coating layer are formed is 10 μm or less in a direction of partinsertion.
 2. The method according to claim 1, wherein each line-shapedSn coating layer has a width of from 1 to 500 μm, and an intervalbetween adjacent line-shaped Sn coating layers is from 1 to 2000 μm. 3.The method according to claim 1, wherein the transferring of theprojections is prior to the plating.
 4. The method according to claim 1,wherein the Cu—Sn alloy coating layer and the Sn coating layer areformed in this order on the surface of the copper sheet, and part of theCu—Sn alloy coating layer is exposed on an outermost surface of themating-type connecting part.
 5. The method according to claim 4, whereinthe Cu—Sn alloy coating layer has an average thickness of from 0.1 to 3μm, and the Sn coating layer has an average thickness of from 0.2 to 5.0μm.
 6. The method according to claim 4, wherein a Ni coating layer isformed between the surface of the copper sheet and the Cu—Sn alloycoating layer.
 7. The method according to claim 6, wherein a Cu coatinglayer is formed between the Ni coating layer and the Cu—Sn alloy coatinglayer.
 8. The method according to claim 6, wherein a Cu coating layer isformed between the surface of the copper sheet and the Ni coating layer.9. A method for producing a mating-type connecting part, the methodcomprising: stamping a copper sheet into a predetermined shape, pressinga surface of the copper sheet with a die which has a plurality ofparallel lines of projections formed on a pressing surface of the die,thereby transferring the projections to the surface of the copper sheetand forming depressions during, before, or after the stamping, thedepressions being formed as two sets of parallel lines which cross eachother in a grid pattern, plating the surface of the depressions-madecopper sheet with at least tin to form a Sn coating layer, and reflowingthe at least tin after the plating such that a surface of the Sn coatinglayer is smoothed and line-shaped Sn coating layers are each formed andexposed in each of the depressions of the copper sheet, and that a Cu—Snalloy coating layer is formed and exposed adjacent to each side of eachline-shaped Sn coating layer, wherein a maximum height roughness Rz of asurface of the mating-type connecting part on which the line-shaped Sncoating layers and the Cu—Sn alloy coating layer are formed is 10 μm orless in a direction of part insertion.
 10. The method according to claim9, wherein each line-shaped Sn coating layer has a width of from 1 to500 μm, and an interval between adjacent line-shaped Sn coating layersis from 1 to 2000 μm.
 11. The method according to claim 9, wherein thetransferring of the projections is prior to the plating.
 12. The methodaccording to claim 9, wherein the Cu—Sn alloy coating layer and the Sncoating layer are formed in this order on the surface of the coppersheet, and part of the Cu—Sn alloy coating layer is exposed on anoutermost surface of the mating-type connecting part.
 13. The methodaccording to claim 12, wherein the Cu—Sn alloy coating layer has anaverage thickness of from 0.1 to 3 μm, and the Sn coating layer has anaverage thickness of from 0.2 to 5.0 μm.
 14. The method according toclaim 12, wherein a Ni coating layer is formed between the surface ofthe copper sheet and the Cu—Sn alloy coating layer.
 15. The methodaccording to claim 14, wherein a Cu coating layer is formed between theNi coating layer and the Cu—Sn alloy coating layer.
 16. The methodaccording to claim 14, wherein a Cu coating layer is formed between thesurface of the copper sheet and the Ni coating layer.